Using no more than sail-bearing rafts, these travelers carried goods almost 4,000 miles.

More than a thousand years ago, Ecuadoran traders were regularly traveling to western Mexico and back, a round trip of about 3,800 miles. And they were probably going by way of sail-bearing balsa rafts, according to an analysis conducted by Leslie Dewan, an MIT doctoral candidate in nuclear engineering, and her colleagues.

Archaeologists have long wondered why copper work and other metalwork in a style typical of ancient South America appears in western Mexico but nowhere in between the two areas. This absence suggested a sea-based trade, so Dewan’s group decided to explore whether such lengthy voyages were feasible. They based their mathematical study of seaworthiness on 16th-century European explorers’ descriptions of Native American trading vessels in western Mexico. The explorers wrote of seeing rectangular, two-sailed vessels made of balsa, a wood native to Ecuador, tied together with a hemplike fiber. Reaching about 35 feet in length, the rafts could probably have borne up to 30 metric tons of cargo—as much as 19th-century barges did in the Erie Canal. The team’s analysis, published last spring in the Journal of Anthropological Research [abstract], also evaluated the role of wind and water currents, concluding that the traders may have spent a few months in Mexico and returned when currents shifted.

Dewan’s team is preparing to sail a small balsa raft between Boston and Provincetown, Massachusetts, this spring. Their ultimate goal is to construct an actual-size model for the trip from Ecuador to Mexico—just as they theorize it was done 1,300 years ago.